Human immunodeficiency virus (HIV)-1 is the causative agent of acquired immunodeficiency syndrome (AIDS). HIV-1 entry into target cells is initiated by a high-affinity binding of HIV-1 envelope gp120 glycoprotein to the primary receptor CD4, and the subsequent interaction of CD4-bound gp120 with the appropriate chemokine receptor (co-receptor), either CXCR4 or CCR5. See, e.g., Feng et al. (1996) Science 272:872-877; Deng et al. (1996) Nature 381:661-666. Most HIV strains are dependent upon the CD4/CCR5 receptor/co-receptor combination to gain entry into a cell and are termed CCR5 (or R5) tropic. Some viral strains however are dependent on the CD4/CXCR4 receptor/co-receptor combination and are termed CXCR4 (or X4) tropic, while others can utilize both the CD4/CCR5 and CD4/CXCR4 combinations and are termed dual (or R5/X4) tropic.
The engagement of gp120 with the correct co-receptor leads to the exposure of the viral gp41 fusion peptide (FP), which inserts into the target cell membrane producing a so-called pre-hairpin intermediate bridging the viral and host cell membranes. In the pre-hairpin structure, the N-terminal heptad repeat (NHR) of gp41 forms a trimeric coiled-coil, onto which the C-terminal heptad repeat (CHR) of gp41 folds to form a 6-helical bundle (also called trimer-of-hairpins). The formation of trimer-of-hairpins drives the two membranes in close apposition, and ultimately leads to membrane fusion and the release of the viral nucleocapsid core into the cells. See, e.g., Chan et al. (1997) Cell 89:263-273; Eckert et al. (2001) Annu Rev Biochem 70:777-810.
The pre-hairpin intermediate has a relatively long half-life (see, e.g., Munoz-Barroso et al. (1998) J Cell Biol 140:315-323) and constitutes a target for active new drug development. Several peptides derived from the NHR and CHR regions of gp41, designated N- and C-peptides, respectively, have potent anti-HIV fusion activity, through blocking the formation of trimer-of-hairpins or other mechanisms. Examples of such anti-HIV fusion C-peptides are SJ-2176, T-20, N36 and C34. (Liu et al. (2005) J Biol Chem 280:11259-11273). Such peptide fusion inhibitors can potentially become anti-HIV therapeutics. For example, fuzeon (also known as T-20 or enfuvirtide), one of the synthetic C-peptides, was the first peptide fusion inhibitor to gained Food and Drug Administration (FDA) approval for use to treat AIDS (Rockstroh et al. (2004) Antimicrob Chemother 53:700-702).
At least some peptide fusion inhibitors appear to tolerate being used in protein conjugation or membrane-anchoring. For example, an albumin-conjugated C34 peptide fusion inhibitor exhibited improved anti-HIV activity in vivo (Stoddart et al. (2008) J Biol Chem 283:34045-34052). Other examples include a membrane-anchored N-peptide made by conjugating with a fatty acid (Wexler-Cohen et al. (2009) PLoS Pathog 5, e1000509) and a C-peptide made by addition of a cholesterol group (Ingallinella et al. (2009) Proc Nat'l Acad Sci USA 106:5801-5806), which also exhibited improved anti-HIV activity. Furthermore, direct membrane-anchored (surface expressed) peptide fusion inhibitor exhibited potent anti-HIV activities in vitro (see, e.g., Hildinger et al. (2001) J Virol 75(6):3038-42 and Egelhofer et al. (2004) J Virol 78(2):568-75), and importantly, conferred a survival advantage to cells expressing a peptide fusion inhibitor both in vitro and in vivo in the presence of simian immunodeficiency virus (SIV) or HIV (see, e.g., Kimpel et al. (2010) PLoS One 5(8); Zahn et al. (2008) Gene Ther 15(17):1210-22).
Entry of HIV-1 into target cells can be prevented by targeted disruption or knock-out of the HIV-1 coreceptors. U.S. Patent Publication Nos. 20080159996 and 20100291048 disclose nuclease-mediated genomic modification of CCR5 and CXCR4. However, the disruption or knock-out of viral receptors such as CXCR4 may have undesired consequences in some circumstances, for example, a hampered response to its natural chemokine ligand, CXCL12, which is involved in T cell homing and inflammatory responses.
Thus, there remains a need for the development of novel anti-HIV strategies to prevent HIV infection without disruption of the normal chemokine receptor functions, for instance by developing methods and compositions for attachment of a peptide fusion inhibitor to a cell surface (e.g., viral) receptor to inhibit viral entry and treat viral diseases.